One common application for thermal sensors is in thermal (infrared) detection devices such as night vision equipment. One class of thermal detection devices includes a focal plane array of infrared detector elements or thermal sensors coupled to an integrated circuit substrate with a corresponding array of contact pads between the focal plane array and the integrated circuit substrate. The thermal sensors define the respective picture elements or pixels of the resulting thermal image.
One type of thermal sensor includes a pyroelectric element formed from a pyroelectric material that changes its electrical polarization and capacitance in response to thermal radiation, such as barium strontium titanate (BST). An infrared absorber and common electrode assembly is disposed on one side of the pyroelectric element and comprises an optical coating disposed over a common electrode. A sensor signal electrode is disposed on the opposite side of each pyroelectric element. The infrared absorber and common electrode assembly typically extends across the surface of the focal plane array and electrically couples each pyroelectric element through the common electrode. Each infrared detector element or thermal sensor is defined, in part, by a portion of the infrared absorber and common electrode assembly and a respective sensor signal electrode, which constitute capacitive plates, and a pyroelectric element, which constitutes a dielectric or insulator disposed between the capacitive plates.
To maximize thermal response and enhance thermal image accuracy, each pyroelectric element of the focal plane array is preferably isolated thermally from adjoining pyroelectric elements so that the sensor signal accurately represents incident infrared radiation associated with each thermal sensor. Thermal isolation between adjoining thermal sensors, known as inter-pixel thermal isolation, improves the accuracy and quality of the resulting thermal image. Several approaches have been used to improve inter-pixel thermal isolation in a focal plane array.